Add RX OOO completion feature

The RX out of order completion feature, allows to complete RX
descriptors out of order, by keeping trace of all free descriptors in
the separate array.

Submitted by: Michal Krawczyk <mk@semihalf.com>
Reviewed by: byenduri_gmail.com
Obtained from: Semihalf
Sponsored by: Amazon, Inc.
Differential Revision: https://reviews.freebsd.org/D12855